1. Field of the Invention
The invention relates to an electrically operated charge-air compressor for supplying combustion air of an internal combustion engine.
2. Description of the Prior Art
It is known to increase the power density of an internal combustion engine by compressing the charge air required for combusting the fuel using an exhaust-gas turbocharger, which comprises a turbine and a compressor that is operated in the charge-air input duct of the engine. Particularly in motor vehicle drive mechanisms, exhaust-gas turbochargers have the disadvantage of delayed and inadequate response at low engine rpm. To improve the response of the exhaust-gas turbocharger, it is known for the exhaust-gas turbocharger to be reinforced by an electrical auxiliary drive mechanism. This can be attained for instance by means of an electric motor integrated with the exhaust-gas turbocharger; at low engine rpm, this electric motor provides a reinforcing drive of the shaft of the exhaust-gas turbocharger. However, not only must the electric motor be capable of withstanding high rpm, but the electrical power consumption is also high, because of the high moments of mass inertia of the exhaust-gas turbocharger turbine, which is made of high-temperature-resistant steel.
For overcoming these disadvantages, it is known, for instance from U.S. Pat. No. 6,029,452, to operate an electrically operated charge-air compressor, also known as an electrically operated auxiliary charger or an electric turbocompressor in the charge-air input duct of an internal combustion engine in series with a conventional exhaust-gas turbocharger. This has the advantage that the electric turbocompressor, inserted separately into the charge-air input duct, can be optimized for the lowest rpm range of the engine, and because of the markedly lesser moment of mass inertia, its power consumption is markedly less. In the high rpm and throughput range, a bypass embodiment is employed in order to deliver the charge air directly to the exhaust-gas turbocharger, completely bypassing what is then the inactive electric turbocompressor. To that end, a butterfly valve is used, which diverts the flow of charge air into the bypass conduit so that it no longer flows through the electrically operated turbocompressor. However, the bypass embodiment is not optimal in terms of the thermodynamic requirements and is very complicated and expensive in terms of assembly, size and expense for the entire system.
The electrically operated charge-air compressor of the invention overcomes the disadvantages that occur in the prior art and makes it possible for an electric turbocompressor to be operated in the charge-air input duct of an internal combustion engine in series with an exhaust-gas turbocharger, without requiring a bypass conduit for bypassing the turbocompressor. As a result, the entire system can advantageously be optimized thermodynamically. The bypass conduit with the check valve can be omitted. Assembly can be made considerably easier, and both the required space and the costs can be reduced markedly. This is advantageously attained by providing that at medium to high rpm of the engine, the compressor impeller of the electric turbocompressor can be displaced out of a compression portion of the flow conduit for the charge air at least partway into a position of repose, so that at high engine rpm, the charge air can flow quasi-unhindered through the compression portion, without being hindered in doing so by the compressor impeller of the compressor that is now inactive.